So there is this regular effort to run a libre game jam which I know some people here participated in:
Our friends at LibreGameWiki have some details on the past themes. And here is the thread about it on our old forum.
Their main mode of communication seem to be their own IRC network.
This is a pretty cool project I think :)
P.S.: Would there be interest to have a dedicated game jam subsection in this new forum? We will probably not officially organize game-jams ourselves (there are already plenty), but having a place to collaborate and share mght be cool?